1. Field of the Invention
This invention relates in general to the use of thermoplastic polyamide moulding compositions with reduced or strongly reduced formation of solid deposits during thermoplastic conversion into commodity goods in discontinuous processes, in particular injection moulding, and continuous processes such as the extrusion of films, fibers, tubes and jacketings. The polyamide moulding compositions used are based on polyamides containing at least 20% by weight polyamide and/or copolymers with at least 20% by weight polyamide components. The present invention particularly relates to the use of thermoplastic polyamide 12 moulding compositions based on hydrolytically produced polyamide 12, which contains specific compounds in certain quantitative proportions in order to avoid or reduce the formation of monomer deposits. Such produced polyamide moulding compositions according to the present invention do not result in the usual solid deposits and/or during further processing in injection moulding or extrusion.
Polyamides in accordance with the invention are therefore considered polyamides, based on C6–C12-lactames or (ω-amino acids with 4 to 18 carbon atoms, preferably 6 to 12 carbon atoms, or polycondensation products are used, obtained from polycondensation of at least one diamine from the group of aliphatic diamines with 4 to 18 C atoms, cycloaliphatic diamines with 7 to 22 C atoms in combination with at least one dicarboxylic acid from the group of aliphatic dicarboxylic acids 4 to 44 C atoms, cycloaliphatic dicarboxylic acids with 8 to 24 C atoms and aromatic dicarboxylic acids with 8 to 20 C atoms.ω-aminocarboxylic acids or lactames are selected from the group consisting of ε-aminocapronic acid, 11-amino undecane acid, 12-aminododecane acid, ε-caprolactame, enantholactame, laurinlactame. In accordance with the invention it is further possible to use mixtures of those polymerisates or polycondensation products respectively. In accordance with the invention suitable diamines which are combined with a dicarboxylic acid are e.g. 2,2,4- or 2,4,4-trimethylhexamethylenediamine, 1,3- or 1,4-bis(aminomethyl)cyclohexane, bis(p-aminocyclohexyl)methane, m- or p-xylylenediamine, 1,4-diaminobutane, 1,5-diamino-2-methylpentane, 1,6-diaminohexane, 1,8-diaminooctane, 1,9-diaminononane, 2-methyl-1,8-diaminooctane, 1,10-diaminodecane, 1,12-diaminododecane, cyclohexyldimethylenediamine, and the dicarboxylic acids selected from the group of succinic acid, glutaric acid, adipic acid, suberic acid, pimelic acid, suberic acid, acelaic acid, sebacic acid, dodecanedicarboxylic acid, octadecanedicarboxylic acid, 4-cyclohexanedicarboxylic acid, terephthalic acid, isophthalic acid, and the naphthalene dicarboxylic acids.
Specific examples of the polyamides used in the context of the present invention and the additionally added (co)polyamides to the blends or alloys for the moulding compositions in accordance with the invention respectively, are therefore homo- and copolyamides from the group of PA 6, PA 66, PA 11, PA 46, PA 12, PA 1212, PA 1012, PA 610, PA 612, PA 69 PA 9T, PA 10T, PA 12T, PA 12I, mixtures thereof or copolymers based on monomers used. Preferred are, in accordance with the invention, also copolyamide PA 12T/12, PA 10T/12, PA 12T/106 and PA 10T/106. Furthermore are e.g. PA 6/66, PA 6/612, PA 6/66/610, PA 6/66/12, PA 6T/66, PA 6/6T, PA 6/6I, PA 6I/6T or mixtures thereof or mixtures such as PA 12/MACMI, PA 66/6I/6T, MXD 6/6 preferred polyamide moulding compositions as well.
In accordance with the invention the polyamide moulding compositions may also contain polyamide blockcopolymers, particularly polyamide 12-blockcopolymers which contain polyester-, polyether-, polysiloxane-, polycarbonate-, polyacrylate-, polymethacrylate- or polyolefin segments as further components beside a proportion of at least 20% polyamide components, particularly polyamide 12 components. Representatives of this class of polymers are polyether amides, polyetheresteramides und polyester amides:
2. Description of Related Art
In the state of equilibrium polyamide melts show certain concentrations of linear and, if necessary, cyclic monomers and linear and cyclic oligomers and also water. The low-molecular components have an influence on the processibility of the products. They lower the viscosity of the polymer melts. With injection moulding and extrusion processes residual monomers, particularly lactames, and cyclic oligomers may evaporate and may cause disturbance due to the formation of solid deposits and coverings (scales).
Therefore, like all polymers formed by step growth reactions, polyamides naturally contain low concentrations of rest monomers and oligomers.
In general, the monomers and/or oligomers are removed from the polyamide granulates by static or dynamic extraction with water, methanol, ethanol, ethanol/water or chloroform. Following DIN 53378 (German Industry Standard) and DIN ISO 6427 respectively, polyamide powders of specific grain size and certain conditions are to be extracted with methanol. The monomers always occur in a mixture with oligomers. Depending on type and molar mass, those can be removed more or less completely from the polyamides depending on extraction conditions.
With the amorphous, semi aromatic copolyamides comes the problem, that the extraction with common solvents such as methanol or methylenechloride does not produce considerable amounts of extraction due to the high glass transition temperature of the products and that the polymer material blends together when using high boiling points alcohols.
With the semi aromatic polyamides and the so-called HT (high temperature)-polyamides such as PA6I/6T, apart from residual monomers and oligomers, also the low-molecular decomposition products formed during production and processing must be considered with regard to deposit formation.
It is therefore desirable to remove or avoid the above mentioned low molecular components, so that no solid deposits or coverings will be formed in the following thermoplastic processing.
Polyamide 12 (PA 12) is a type of polyamide which is distinguished by it s property profile. Polyamide 12 can be modified in several ways, and the resulting moulding compositions are outstanding thermoplastics in injection moulding and convertible into valuable items of practical use in extrusion processes. Polyamide 12 corresponds to the type of polyamide the properties of which are the least influenced by changes in temperature and humidity.
One problem is that during the common hydrolytic polymerization process/autoclave treatment the monomer turnover is only 99.5% and the remaining residual lactame is hardly soluble in the polymer, so that, particularly in processing from melts, but also in the later use the lactam 12 (LC12) is sweat out and sublimed, especially on cooled faces, e.g. the surfaces of tools and prefabricated parts where it comes to the formation of deposits. Particularly due to the high melting point of lactam 12 those sublimates often form irritating deposits which, particularly when further additives migrate to the surface, give cause for processing troubles with surface damaging and production interruption. So-called “black spots” can also be formed. Well-known measures taken for reduction and elimination of the rest content of lactame 12 are, e.g. the melt- and solid phase after condensation including vacuum, liquid extraction processes or recrystallization from alcoholic solution. These processes where the lactame evaporates under thermal influence may as well be disrupted by the lactame sublimate. Furthermore the lactame smoke is highly inflammable and the processes require certain precautionary measures. Furthermore the additional thermal stress can damage the polymer. In thermoplastic processing of polyamide 12 (PA12) moulding compositions by injection moulding and by extrusion, the formation of solid deposits, particularly those consisting of lactame 12 (LC12), has a detrimental effect.
Other polyamides also tend to the formation of deposits when they are exposed to higher temperatures, e.g. during thermoplastic conversion. Depending on the type of polyamide these deposits are composed of varying parts of monomers, oligomers and various decomposition products emerging during processing.
Thus simple, cost saving measures are wanted to avoid the formation of solid deposits or coatings in the subsequent thermoplastic processing of polyamide moulding compositions which in particular are based on polyamide, particularly preferred polyamide 12 or a copolymer or polyamide respectively, which contains polyamide components, especially polyamide 12 components as well.
The generally used process to give polyamides and particularly polyamide 12 a higher standard of flexibility, elasticity and finish is to disperse plasticizers in larger amounts, i.e. more than 10% by weight. For polyamide 11 and polyamide 12 typical plasticizers such as sulfonamides, phenol derivatives and arylphosphites are suggested (see EP 0 748 847 B1). However, plasticizers in amounts well below 10% by weight are avoided, because with these low amounts brittleness and hardening of the polymers occurs (“Anti-plasticizer-effect”). Only at higher concentration the plasticizers take effect (see Ullmanns Encyclopedia of technical chemistry, 4. Ed., Vol. 24, p. 357, “plasticizer”).
U.S. Pat. No. 6,506,830 B1 describes antistatic polyamide moulding compositions with common plasticizers according to the state of the art. The plasticizer concentrations correspond to the usually high plasticizer concentrations (see claim 9; up to 30% by weight). Although U.S. Pat. No. 6,506,830 B1 claim 9 mentions a plasticizer amount of up to 30% by weight and therefore theoretically all concentrations are contained, it is well-known from the literature that small plasticizer additions are regarded as rather giving contrary results due to the “anti-plasticizer-effect” when considering an improvement of material properties. However, in the same context as the plasticizers lactames are mentioned which are the main cause for the formation of deposits.
EP 0 748 847 A2 describes common plasticizer containing polyamide moulding compositions recognisable by the high plasticizer concentrations (preferably 8 to 20% by weight). Furthermore, the advantageous use of plasticizer mixtures is described. The quoted plasticizers also contain sulfonamides and hydroxybenzoates. However, EP 0 748 847 A2 confines itself to the flexibility and cold impact strength of polyamides. Problems of solid deposits are not mentioned. In contrast to this the evaporation of the plasticizer is quoted as a disadvantage (see p. 2, 1. 58 to p. 3, 1. 3). EP 0 748 847 A2 mentions the surface of the mould, but only in the context of a “nontacky surface” which is in no conjunction with the described problems of solid deposits. Apart from that for plasticizers closest attention is paid to vitrification temperature. However, properties at room temperature or higher temperature which are required for the solubility of the polyamide specific solid deposits are not dealt with.
WO 97/10303 uses plasticizers at concentrations of up to 5% by weight for the improvement of welding properties or the increase of joint line strength of the polyamide moulding compositions. Sulfonamides are used as well. But in the same context as the use of plasticizers lactames are mentioned (see p. 4, 1. 35–36). But just the lactames are the cause of the solid deposits.
WO 01/05888 describes moulding compositions which contain, beside polyacetal, flame proving agents and N-containing compounds that can be low molecular. Sulfonamides and urea derivatives belong to these compounds too. The N-containing compounds strengthen the flame protection and increase the stability of the moulding compositions described. In their function as stabilizers concentrations of up to 2.5% are used.
In accordance with WO 01/05888 the moulding compositions must always contain polyacetal and this reference gives no hint to the described problems of solid deposits. This is plausible, because polyamides can be contained in polyacetal, but never play a dominant role there.
EP 0 388 583 A1 is aimed at the fact that the deteriorated cold impact strength of polyamide moulding compositions due to softening can be balanced by certain polyamides. Common plasticizer-containing polyamide moulding compositions are described here with up to 25% by weight plasticizers.